North Korean refugees (NKRs) are often exposed to traumatic events in North Korea and during their defection. Furthermore, they face sociocultural barriers in adapting to the new society to which they have defected. To integrate previous findings on this mentally vulnerable population, we systematically reviewed articles on the mental health of NKRs in South Korea. We searched for empirical studies conducted in the last 10 years in six online databases (international journals: Embase, PubMed, Scopus, Web of Science; Korean journals: DBPIA, KMbase) through June 2017. Only quantitative studies using new empirical data on the mental health of NKRs were included. We summarized the 56 studies ultimately selected in terms of NKRs' mental health status and three domains of associated factors: pre- and post-settlement factors and personal factors. NKRs had a high prevalence and severity of psychiatric symptoms, particularly post-traumatic stress disorder and depression. We identified nine risk factors consistently found in previous studies, including traumatic experience, longer stay periods in third country, forced repatriation, acculturative stress, low income, older age, poor physical health, and female and male sex, as well as four protective factors, including educational level in North Korea, social support, family relationship quality, and resilience. We suggest that future studies focus on the causal interactions between different risk and protective factors and mental health outcomes among NKRs from a longitudinal perspective. Furthermore, comprehensive policies for NKRs' psychological adaptation are needed, particularly the development of evidence-based mental health interventions.